Extraction of aluminum from silicate rocks and minerals containing aluminum



United States Patent 3,507,629 EXTRACTION OF ALUMINUM FROM 'SILICATE ROCKS AND MINERALS CONTAINING ALUMINUM Henry G. Iverson, Reno, and Harold Leitch, Boulder City, Nev., assignors to the United States of America as represented by the Secretary of the Interior No Drawing. Filed Feb. 10, 1966, Ser. No. 529,170 I WInt. Cl..B.01d 9/02,11./02; (301 17100. US. Cl. 23--299 13 Claims ABSTRACT ,OF THE DISCLOSURE Almostcomplete recoveries of alumina are obtained from various types of aluminum silicate materials having relatively narrow ranges of silica/ base ratios by melting, quenching, and leaching in dilute acid solutions.

3,507,629 Patented Apr. 21, 1970 "ice ing 1700 C. One method for achieving a completely molten and chemically homogeneous liquid mass, but not necessarily the only way, is to increase the temperature N from done by the Bureau of Mines of the Department of the Interior, and the domestic title-to the invention is in the Government.

. This invention relatesto the extraction of. aluminum.

from aluminum-bearing siliceous materials.

As used in the specification and claims, the phrase aluminum-bearing siliceous materials includes aluminum silicate compounds, minerals and mixtures, andmix. tures of silica or silica compounds with aluminum-bearing minerals, compounds and mixtures.

Although the United States has vast low grade resources of aluminum in the form of anorthosite and other aluminum-bearing siliceous materials including clays,

ky nite and. s l m' n te,.. s. d p ndent. on fore gn sources of aluminum ore in the form of high grade bauxite for over 80 percent of its aluminum production. Lack of economic processes for treating the low grade resources prohibits the industrial use of these sources.

, .Anobject of this invention is to provide a reliable and economical procedure to recover virtually all of the aluminum contained in aluminum-bearing siliceous materials in a solid chemical form-thatcan be readily converted to alumina (A1 0 'A further object is to provide a procedure for preparing these materials in a highlyfractured, friable condition.

It has now been discovered that the relatively insoluble aluminum values in these siliceous materials may readily be leached from the materials with hot sulfuric acid soluof the melt to 100 C. after the disappearance of any unmelted material, and to maintain the molten mass at the increased temperature for 5 minutes. Melting temperatures and the time held in the molten state will obviously vary from one raw material to another. The molten mass is then rapidly cooled or quenched by, for

"example, pouring it into a pool of water large enough leached with a hot-to-boiling acid solution. Particle sizes of 35-mesh or coarser may sufiice for high aluminum value extractions, but 65-mesh or finer sizes are more advantageous for fast extractions. Although other inorganic acids such as nitric acid and hydrochloric acid may be employed, dilute sulfuric acid is the best leaching medium for the particles. For example, extraction with hydrochloric acid results in the dissolution of calcium that is contained in most raw materials which must be removed before the desired aluminum compounds can be precipitated from the pregnant leach solution. When using sulfuric acid supplied in such a quantity so that 1.26 to 1.68 grams of acid are present per gram of solid, an 8 to 16 /3 volume percent acid solution is sufiicient.

.Contact times .of 15m 30 minutes with such as acid solution will leach out 95 to 99 percent of the contained aluminum. Longer contact times and higher acid strengths each alone or taken together decrease the Si0 and CaO content is the pregnant solution.

After leaching, the pregnant solution is readily separated from the solid residue by the usual thickening and filtering procedure (e.g. the addition of settling agents such-as hideglue or starch);-deeantation-ofclear-pregnant solution, filtration of remaining thickened slurry; and washing of the filter cake with water to remove en trained solution.

tions after forming these materialsas amorphous solids by completly melting and quenching.

Further objects and advantages will be had from the following description of the process.

Raw materials such as albite,'anorthite, anorthosite, and mixtures thereof are first crushed to a size that is suitable for melting. Except as the variations in size may Aluminum compounds can be separated from clear pregnant leach solution by evaporation of the solvent or chemical precipitation. Although chemical precipitation by, for example, neutralization may be employed, most of Y the low grade-aluminum-bearing siliceous materials when leached with sulfuric acid yield a clear leach solution which, when subjected to autoclaving under various temperatures and pressures, precipitates out a sodium aluminum sulfate having the approximate formula NaAl (S0 .(OH) the precipitate being readily filtered and water washed. This sulfate can be easily converted to the valuable compound alumina.

An important aspect of the process resides in the SiO :CaO weight ratio in the raw charge material. A ratio of 3:1 to 8:1 and preferably within 4:1 to 6:1 is necessary to the high extraction of aluminum and to the formation of slurries that can be readily separated into residual solids and clear pregnant solutions, from which aluminum, in the form of compounds, can subsequently Analysis, percent be recovered. Although many raw materials inherently Feed material A1203 sioz N820 C30 F9703 contain the desired ratio, silicateor CaO-contammg ma- C m i th 28 53 10 6 2 3 terials must be added to some charges. g g gggg g g:: 29 52 12 4 5 The followmg examples illustrate ways in which the Minnesota anorthosite... 32 4s 15 3 1.9 New York anorthosite 26 53 11 5 1. 5

principle of the invention has been applied, but not to be construed as limiting its scope.

Pregnant solution impurities, gJlOO g. A1203 Materials melted A1203 SiOz added, SiOzzCaO extracted, Test Anorthosite wt. pct. wt. ratio pct. S102 F6203 CaO 1 Not analyzed. 2 Slurry gelled, no analysis possible.

EXAMPLE 1 EXAMPLE 3 Leaching of melted and quenched albite and anorthite Effect of leach variables minerals and mixtures Albite and anorthite, and mixtures of these minerals, were melted and the molten masses were quenched in water. 50 gram samples of the melted and quenched The elfects of sulfuric acid concentration, weight ratio of acid to feed, time, temperature, and size of feed solids on leaching melted and water-quenched California anorthosite having the composition set forth in Exprod-ucts ground to minus 65-mesh were leached open to ample 2 are shown below:

Grams Pregnant; solution H28 04 impurities, Particle Leach Acid conper gram Leach A1203 g./10 0g. AlzOa mesh solution centration, anorthosite time, extracted,

Test Run size temp., 0. pct. e hrs pet. S101 FerOa (3210 A 1 65 100 4 1. 12 25 I 75 6. 5 1. 4 10. 1 2 65 100 16 l. 12 25 99 3. 4 1. 2

1 Not analyzed.

air with 288 ml. of 16volume percent sulfuric acid at As can be seen from tests A, B and-D, respectively, C. to boiling temperatures for 15 minutes, using 50 aluminum-value extraction varies with the acid conabout 1.68 grams of sulfuric acid per gram of solids and centration, the acid-to-feed ratio and leach'solution temthe following results obtained: perature. Test B shows that more aluminum values can Material melted Pregnant solution impurities, g.

A; g. A120 Albite, Anorthite, S102: GaO extracted, wt. pct wt. pct. wt. ratio p S10 Fe O QaO Not analyzed. I 9 Slurry gelled, no analysis possible.

, EXAMPLE 2 be extracted the smaller the ore particle size. In regard Leaching of melted and watepquenched to leaching time, as shown 1n test C, maximum leaching Y anorthosite appears to be achieved at the end of one-half hour.

y EXAMPLE 4 I The effect of leaching time on the impurities present in the resultant leach liquor are shown below. California Samples of California, Wyoming, Minnesota and New 70 York anorthosite of various chemical compositions were melted, quenched, ground, and leached under the same conditions as in Example 1. Silica (SiO was added to Wyoming and Minnesota anorthosites before melting. The results are shown below:

- anorthosite having the composition set forth in Example 2 and with a mesh size of 65 was the solid feed. A

75 16% by volumn sulfuric acid leach solution was employed and leaching Was carried out at the boiling point of the solution. I q

Impurities in pregnant solution, grams per 100 Ratio A1203 grams A120 g. H2804 per extracted, Time hours g. feed percent S102 CaO 0.25 2. 24 99. 2 2. 92 6. 13 1.0.- 2. 24 99. 6 20 5.02 4.0 2. 24 98. 6 l 2. 73 1.0 2. 24 99. 6 20 5. 02 4. 2. 24 99. 6 10 2. 20 .2 1. 68 99. 6 2. 64 3. 32 0. 2. 24 99. 2 2. 92 6. 13 1 2. 24 99. 6 20 5. 02 4 2. 24 98. 6 10 2. 73 1 2. 24 99. 6 20 5. 02 4. 2. 243 99. 6 l0 2. 20 .25 1. 68 99. 6" 2. 64 3. 32 16 0 1. 68 99. 6 29 1.02 .2 2. 24 99. 2 2.92 6. l3 2. 24 99. 6 20 2. 39

The above table shows that after the maximum amount of A1 0 has been extracted from the raw material, continued contact of the material with the leaching medium reduces the amount of CaO and SiO in the pregnant leach liquor, thereby providing the A1 0 in a more desirable state in the leach liquor.

EXAMPLE Leaching of mixed compounds Silica, alumina and calcium oxide were mixed together, subsequently melted and quenched.

The quenched products were ground to minus 65-mesh and leached at 90 C. to the boiling point for 30 minutes with 16% sulfuric acid solution using about 1.68 grams of H 50 per gram of feed. The results are given in the table below.

Material leached, chemical analysis, wt.

percent A1203 Wt. ratio, extracted,

S102 CaO SiOzOaO percent 1 Gelled-could not filter.

Example 5 illustrates that aluminum extraction by the process of this invention is not limited to specific minerals, but is equally applicable to chemical compounds and mixtures of the same. Furthermore, the process is not necessarily dependent on the physical state (including, but not limited to crystal structure, molecular arrangement and purity) of the feed material. Since the charges are completely melted, the nature of the aluminum bearing constituents, whether crystalline or amorphous or whether present as one chemical compound or as several individual compounds, is not significant provided the combined chemical analysis conforms to the desired SiO to CaO weight ratio. Therefore, not only is the process applicable to minerals and mixtures of minerals such as anorthosite, albite and anorthite, but may also be employed with materials such as siliceous bauxite, kyanite, silliminate, kaolin and other clays, chemical or physical mixtures of alumina, silica and calcium oxide. Alkali metal oxides or silicates can be present in the raw materials and do not deleteriously affect the process.

By forming the raw material as an amorphous solid through complete melting and quenching, an intermediate product is arried at that is easily handled, crushed and leached of aluminum. The pregnant leach solution can then be readily separated from solid residue, and the aluminum easily precipitated from the solution in highly desirable for-m.

Although the particular process is well adapted to carry out the objects of the present invention, it is to be understood that various modifications and changes may be made all coming within the scope of the following claims.

What is claimed is:

1. A process for separating aluminum values from a particulate, aluminum-bearing material containing in physical or chemical admixture SiO and CaO which comprises adjusting the proportions of SiO and CaO to obtain a ratio of about 3 to about 8 parts by weight of SiO to 1 part by weight of CaO, completely melting said mate; rial to form a fluent liquid, quenching and cooling said melted material at a rate sufficiently rapid to form amorphous solid material and to prevent formation of crystalline solids therein, leaching aluminum values from said solid material with a hot-to-boiling relatively dilute acid solution, said acid being chosen from the group consisting of sulfuric, hydrochloric and nitric acids, separating pregnant leach solution from solid residue, and precipitating an aluminum compound from said separated pregnant leach solution.

2. The process of claim 1 wherein said aluminumbearing material contains from about 4 to about 6 parts by weight of Si0 to 1 part by weight of CaO.

3. The process of claim 1 wherein said aluminumbearing material also contains Na O and wherein said material contains more than about 3 parts by weight of SiO to 1 part by weight of CaO plus Na O.

4. The process of claim 3 wherein said acid solution comprises sulfuric acid solution.

5. The process of claim 4 wherein said precipitation step comprises autoclaving said separated pregnant leach solution to precipitate therefrom a basic sodium aluminum sulfate having the approximate formula 6. The process of claim 5 wherein said amorphous solid material of claim 1 is pulverized to minus 65 mesh before being leached.

7. The process of claim 4 wherein said amorphous solid material is contacted with said acid solution for a period of time substantially longer than that required to dissolve a maximum amount of the aluminum values present in the aluminum-bearing siliceous material whereby the Si0 and CaO contents of the pregnant acid solution are reduced below the respective amounts of SiO,, and CaO present in the pregnant acid solution at the time maximum aluminum dissolution was initially achieved.

8. A process for separating aluminum values from particulate, aluminum-bearing siliceous material comprising establishing a SiO :CaO weight ratio in the said material of from 3:1 to 8:1, completely melting said material to form a fluent liquid, completely quenching and cooling said melted material at a rate sufiiciently rapid to prevent formation of crystalline solids therein and to form an amorphous solid material therefrom, leaching aluminum values from said solid material with a hot-to-boiling relatively dilute acid solution, said acid being chosen from the group consisting of sulfuric, hydrochloric and nitric acids, separating pregnant leach solution from solid residue, and precipitating an aluminum compound from said separated prenant leach solution.

9. The process of claim 8 wherein said material is selected from the group consisting of albite, anorthite, anorthosie, kyanite, bauxite, sillimanite, and aluminumbearing clays.

10. The process of claim 9 wherein said amorphous solid material is contacted with said acid solution for a period of time substantially longer than that required to dissolve a maximum amount of the aluminum values present in the aluminum bearing silicious material whereby the Si0 and CaO contents of the pregnant acid solution are reduced below the respective amounts of SiO and CaO present in the pregnant acid solution at the time maximum aluminum dissolution was initially achieved.

3,507,629 a a s .7 a v 11. The process of claim 8 wherein the SiO ICaO ratio 3,116,973 1/1964 [Haden 23-123 X is established at from 4:1 to 6:1. 3,143,392 7 8/1964 Laeman 23 1 2 3 9. The process of claim 8 wherein said material is 3,216,792 11/1965 Udy 23- 123 selected from the group consisting of al-bite, anorthite, 3,226,189 12/ 1965 Bretsznajder 23-123 anorthosite, kyanite, bauxite, sillimanite, and aluminum- 7 bearing clays. 5 v FOREIGN PATENTS 12. The process of claim 11 wherein said acid solution 223 794 9/1959v Australia. comprises a sulfuric acid solution. 937,328 9/1963 Great Britain 13. The process of claim 12 wherein said amorphous 1 159:419 12/1963 Germany a solid material is pulverized to minus 65 mesh before 10 being 1 NORMAN YUDKOFF, Prlmary Examiner References Cited s. J. EMERY, Assistant Examiner UNITED STATES PATENTS 2,243,060 5/1941 Fulda 23---305 X CL 2,958,580 11/1960 Lowenstein 23 123 15 12, 02, 305,123 3,011,878 12/1961 Lackey 23123X p 7 

